People involved at OAB: Bonifazi, Bragaglia, Tosi.
Open clusters (OC's) are excellent tools to understand the evolution of the disk of our Galaxy from both the chemical and structural points of view. Many of the existing chemical evolution models are able to reproduce well the present-day situation, but differ significantly in the ``history" of the chemical enrichment (hence in the involved processes). In particular, they differ in the predictions for the evolution of the abundance gradients: does the gradient slope steepen or flatten with time? From the OC's we can extract fundamental information, since they can be used to describe the run of the various elemental abundances at different ages.
In order to study in more detail the metallicity and age distribution with galactocentric distance, we are analyzing with great accuracy a large sample of open clusters (our goal is to have at least 30 OC's) at various Galactic locations and covering a wide range in age and metallicity. Age, distance modulus, reddening and approximate metallicity of the clusters are derived from their Color-Magnitude Diagrams (CMDs) using the synthetic CMD technique, developed by Tosi at the OAB, and further constrained by the observed luminosity functions. Precise and homogeneous elemental abundances are determined from high resolution spectroscopy.
During 2003, we have published our findings on Cr 110 (Bragaglia & Tosi 2003), completed the interpretation of NGC 6939 in terms of evolutionary parameters (Andreuzzi et al. 2004) and proceeded in that of Be 29 (Tosi et al., submitted in 2004).
Up to now only about 25 % of the old OC's have ever been studied with high resolution spectroscopy, and only a handful have abundances of elements other than iron. To widen the sample, we have obtained high-res spectra of red clump stars in a dozen of OC's, with FEROS@1.5m ESO, SARG@TNG, and UVES@VLT. Three clusters have been analyzed and published (NGC 2506, NGC 6134, IC 4651; Carretta et al. 2004). Furthermore, FLAMES@VLT GTO observations have been completed (3 nights, PI Pallavicini, OAPa) for three more old clusters (Cr 261, Mel 66, and NGC 2506), and a proposal to observe 10 more open clusters has been approved, also on FLAMES@VLT (in collaboration with S. Randich et al.).
Finally, medium resolution spectra for 20 stars in Be 29 have been obtained with MOS@TNG, and membership based on radial velocity has been determined (Bragaglia, Held & Tosi 2004).
This research is in collaboration with Carretta, Gratton, Held (INAF-Padova Obs.), Marconi and Andreuzzi (INAF-Roma Obs.), Randich (INAF-Arcetri Obs.), Carraro (Padova Univ.) and Pallavicini (INAF-Palermo Obs.).